Conventionally, as a local anesthesia, surface anesthesia, infiltration anesthesia, conduction anesthesia and the like are known. Among them, the surface anesthesia is an anesthesia in which an anesthetic agent is applied or sprayed onto the mucosal membrane or skin whereby to be adhered or infiltrated, which is conducted in order to alleviate the pain of an injection needle in the following infiltration anesthesia or conduction anesthesia by injection, and is mainly applied for dental treatment of children and the like.
The infiltration anesthesia is a method that anesthetizes an infiltrated part by injection, which is a partial anesthesia, and is used when dental extraction or tooth drilling is conducted in dentistry, or when simple incision operation is conducted in surgery, and the like.
In addition, the conduction anesthesia is a method that anesthetizes even to the tip part on which the nerve runs by injecting an anesthetic agent in the vicinity of the nerve. In dentistry, the conduction anesthesia is a method that anesthetizes from back teeth to anterior teeth on the to-be-anesthetized side by injecting an anesthetic agent mainly around the nerve that enters the bone of the mandible.
A local anesthetic drug is generally classified into an ester type, an amide type or anilide type. Examples of the ester type include benzoate esters such as cocaine, tropacocaine, procaine, tetracaine, piperocaine and stovaine, alkoxybenzoate esters such as cyclomethycaine and parethoxycaine, aminobenzoate esters such as methyl paraaminobenzoate and ethyl paraaminobenzoate. In addition, as the amide or anilide type, lidocaine (Xylocaine) and the like are known.
These anesthetic drugs are constituted as a local anesthetic agent by further blending a vasoconstrictive drug such as catecholamines including epinephrine (adrenaline) and norepinephrine for the purpose of sustaining the effects; a preservative stabilizer such as an antioxidant, e.g., butylhydroxytoluene, gallic acid esters, and the like and a stabilizer agent, e.g., gelatin, agar, starch, thiourea, citric acid, L-methionine, glutamic acid, fructose, sucrose, lactose, thioglycerin, and the like; or, a sweetener, a thickening agent and the like particularly for an oral surface anesthetic agent and the like.
As an improvement in the surface anesthetic agent, a conventional method of enhancing the persistence (for example, Patent Documents 1, 2 and 5), a method of rapidly releasing an anesthetic after operation (for example, Patent Document 3), a method of improving preservative stability of an anesthetic agent (for example, Patent Documents 4 and 5) and the like are proposed. In addition, as an improvement in the fast-acting property of a surface anesthetic agent, a fast-acting percutaneous anesthetic drug in which lidocaine, prilocaine and tetracaine are mixed (for example, Patent Document 6) is proposed. However, in Examples of Patent Document 6, only about 55.7% of the people had pain “0” after 30 minutes of the application.
In addition, proposed are a skin-external agent having an action of ameliorating itching, which is a mixture of a local anesthetic agent, urea, a refreshing agent, alcohol and water (for example, Patent Document 7) and a method of suppressing or ameliorating pain from an surgically closed wound area, which applies a local anesthetic agent onto the outer surface of a wound area (for example, Patent Document 8). However, these documents do not disclose that a fast action property has been improved in a local anesthetic agent to be used.